In many mechanical processes, it is important to position and/or move a piston rod or the like axially under precise control. One such application is die casting. In die casting, the introduction of a molten metal charge into a die is controlled by the precise positioning and movement of a piston by means of a rod. As describe in Pomplas U.S. Pat. No. 3,956,973 the movement and positioning of the rod is controlled with a feedback controller. Information on the position and velocity of the rod is obtained by means of sensors fixed in place in close proximity to the rod. Alternating magnetic and non-magnetic generally circumferential strips are positioned axially along the rod. The disposition of the strips preferably resembles the appearance of threads. The passage of the of alternating strips beneath the sensors produces signals indicative of rod position and velocity. The output of the sensors is a pair of pulse trains with pulses corresponding to the passage of individual magnetic strips. The pulse trains are contained in two signals in quadrature providing direction of travel as well as position information in a conventional manner. Each of the two quadrature signals changes state twice when the rod moves from one magnetic strip to the next. Thus, in an arrangement using two sensors, a maximum of four state changes occur in the distance from the center of one magnetic strip, through a non-magnetic strip, to the center of an adjacent magnetic strip. The resolution of such devices is limited by the width of the strips and the number of sensors used. While such controllers are, in general, successful in providing position information to a feedback controller, some applications require more precise position and velocity information than can be conventionally provided by the abovedescribed system.